Introduction to Electric Circuits

210 Two-port networks

Finally, from Equation (9.14), Y22 = I2/V2 with V~ = 0. We have seen that

with V1 = O,

12- 15V2/125 = 3V2/25

so

Y22 = I2/Vz- (3/25)S

In matrix form we have

[,111 12 -1/25 3/25J V2 ]

9.4 THE HYBRID OR h-PARAMETERS

Set 3: If/1 and V 2 are the independent variables then the dependent variables

are given by:

V1 = h1111 + h12V2 (9.15)

12 --" h21I 1 + h22V 2 (9.16)

In matrix form

[V1]=[ hll hi2][ I1 ] (9.17)

11 kh2a h22] V2

The parameters of this set are called the hybrid or h-parameters and they are

defined as follows:

9 h~l is the input impedance (hi) and is measured in ohms as V~/I1 with

V2 = 0:

hll = (gl/I1)lvz=o (9.18)

9 h21 is the forward current gain (hf) and is a dimensionless ratio of currents

(I2/I~) with V2 = 0:

h2~ = (I2/I~)lv~=o (9.19)

9 h12 is the reverse voltage gain (hr) and is a dimensionless ratio of voltages

(Va/V2) with I~ = 0:

h12 = (Va/V2)I,,=o (9.20)

9 hzziS the output admittance (ho) and is measured in siemens as I2/V2 with

I1=0

h22 = (I2/V2)1,,=o (9.21)

These parameters are used extensively in the small signal analysis of bipolar